One way of producing maps for survey use relies on conducting aerial surveys of the geographic region to be surveyed. It is known that aerial survey photographs are subject to distortions and errors in relation to the geographic area surveyed. The photos obtained during the aerial survey can be used to produce maps, however, the photographic images must be processed to rectify or correct the distortions and errors of the photos by a manual process. This process is referred to as photo rectification. Generally survey photo rectification using manual methods is labour intensive and, therefore, very expensive. Moreover, photo rectification processing of the aerial photos requires a considerable period of time before accurate maps can be produced from the aerial survey photos.
There are various methods which have been introduced to improve the timeliness of photo rectification from which an accurate survey map result can be produced from the aerial photographs. In one manner of aerial photography, a traditional ground survey crew is deployed in the geographic region to be surveyed. The crew surveys selected portions of the geographic region using standard survey equipment such as global positioning sensors (GPS) and survey equipment including transits and lasers to lay actual "photo targets" on the ground. The photo targets provide "known" points on the geographic region that is to be mapped. The photo targets provide a basis for correction of the aerial photoimagery obtained by aerial surveys to permit the end product to be produced, for example, a scaled image map with contour lines and a latitude-longitude grid. Naturally, the more photo targets that are deployed by the ground crew, the more accurate will be the final map survey product produced from the aerial photos.
In another manner of aerial photography, an aerial reconnaissance vehicle or aeroplane can be equipped with a scanning laser to obtain X, Y, Z elevation data points. If the X, Y, Z elevation data points can be related to the geographic region of interest, a survey map comprising a uniform grid for which such X, Y, Z elevation data points define the topography of the geographic region which is surveyed can be produced. Where a scanning laser aerial reconnaissance is used, it is necessary that the optical sensor which captures the laser illumination on the terrain be accurately calibrated and oriented. The optical sensor must be calibrated and oriented in relation to the laser source, as well as in relation to the aerial vehicle which is used to transport the optical sensor and illumination source, such as a laser source, over the terrain to be surveyed.